泛型也可以应用于接口,这边以生成器gennerator为例,生成器是一种专门负责创建对象的类。实际上,这就是工厂方法设计模式的一种应用。不过,当使用生成器创建新的对象时,他不需要任何参数,而工厂方法一般需要参数。也就是说,生成器无需额外信息即可创建对象。
首先生成器接口定义如下:
package com.zy.test;
public interface Generator<T> {
T next();
}
然后定义一些需要的类:
package com.zy.test;
public class Coffee {
private static long count = 0;
private final long id = count++;
public String toString() {
return getClass().getSimpleName() + " " + id;
}
}
class Latte extends Coffee {}
class Mocha extends Coffee {}
class Cappuccino extends Coffee {}
class Americano extends Coffee {}
class Breve extends Coffee {}
现在编写一个类实现Generator<Coffee>接口,它能够随机生成不同类型的Coffee对象:
package com.zy.test;
import java.util.Iterator;
import java.util.Random;
public class CoffeeGenerator implements Generator<Coffee>, Iterable<Coffee> {
private Class[] types = { Latte.class, Mocha.class, Cappuccino.class, Americano.class, Breve.class};
private static Random rand = new Random(47);
public CoffeeGenerator() {
}
private int size;
public CoffeeGenerator(int size) {
this.size = size;
}
@Override
public Coffee next() {
try {
return (Coffee)types[rand.nextInt(types.length)].newInstance();
} catch (InstantiationException | IllegalAccessException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
class CoffeeIterator implements Iterator<Coffee> {
int count = size;
@Override
public boolean hasNext() {
return count > 0;
}
@Override
public Coffee next() {
count--;
return CoffeeGenerator.this.next();
}
public void remove() {
throw new UnsupportedOperationException();
}
}
@Override
public Iterator<Coffee> iterator() {
return new CoffeeIterator();
}
public static void main(String[] args) {
CoffeeGenerator gen = new CoffeeGenerator();
for (int i = 0; i < 5; i++) {
System.out.println(gen.next());
}
for (Coffee c : new CoffeeGenerator(5)) {
System.out.println(c);
}
}
}
输出:
Americano 0
Latte 1
Americano 2
Mocha 3
Mocha 4
Breve 5
Americano 6
Latte 7
Cappuccino 8
Cappuccino 9